Kindergarten students should get familiar with numbers.  For example, to count from 1 to 10 and to pick two numbers from 1 to 9 and make it a 10.

They should visualize the numbers so that they can play with them easily when they are older.

One simple way is to play cards with them.  Take all the cards from Ace, two, to nine and shuffle them (there are 36 cards).  Flip one card out and then the other, until there are two cards that add up to 10.